Vulcanization of butadiene-styrene copolymer



Patented Sept. 23, 1947 No Drawing.

This invention relates to the art of compounding substitutes for natural rubber and. more particularly: to a compounding butadiene-s'tyrene copolymer. 1

Black vulcanizates (products of vulcanization) of ,butadiene styrene copolyrner, frequently designated as Buna S and more recently as G R-S synthetic rubber, of commercially satisfactory tensile strength and otherwise suitable for many practical usesmay be obtained by incorporating certain carbon-black fillers, particularly channel black, in the copolymer prior to vulcanization. There is, however, a large industry andconsumer demand for vulcanized rubber and rubber-like products'of light color, e. g. white, gray, red, etc., that cannotbemet by black vulcanizates containing carbon-black vfillers. In the case of natural rubber, this need has been met successfully by using white or light-colored fillers such 'as calcium carbonate, ,clay, etc. It has been found, however, thatsuch fillers, satisfactorily employed .inmaking non-black vulcanizates from natural rubber, do .notimpart to butadiene-styrene cvpolymer sufficierft. tensile strength'and tear resistance for the manufacture of satisfactory products. g

It is an object of this invention to improve the tear-resisting and tensile properties of vulcanizates of butadiene-styrene cop olymer using as fillers relatively large amounts of non-black metal oxideswhichhave heretofore beenused primarily ln -relatively small amounts aspigments in compoundlngnatural rubber. g .It is a further object of the invention to provide aprocess of compounding butadiene-styrene co,- polymer with, non-blackmetal oxide fillerssoas to obtain vulcan-izatesof improved tensile and tear-resisting properties. Other objects and advantages will appear hereinafter.

. This invention involves the discovery that,- b'y compounding .butadiene-styrene copolymer with non black metal oxidefillers selected from the group consisting of aluminum oxide, titanium 'provement inthe tensile and tear-resisting .properties of the copolymer vulcanizates is obtained. Preferably .from:l5 to 30 parts by weight'of paracoumarone resin are-employed for each 100 parts by weight of the copolymer and f,-rom.20 1,to

siren STATES 1 f 2,427,942 I Y I H I V'ULCANIZATI N oF BUTADIE'NE-STYRENE I I .GOPoLy ER I I Theodore A. Bulifant, Hackensack, N. ,J,, assignor to Allied Chemical. .nye Corporation, .ly'cv'v York, N. Y., a corporation of N ew( York Application am 10, 1944', SerialNo. 521,846

11 Claims. (01. 2 0-41) A vulcanizing agent, usually sulfur' and vul canizing accelerato'rare .clispersed i n the cop'olymer prior to vulcanization. Where metal oxide other than zinc oxideyis employuas the filler, a

metal oxide which activates the accelerator is also incorporated in the cop'olyiner prior to ,vulcanization. 3

I havefound that by compounding jbutadienelstyrene copolymer with such metal oxide Yiillers are paracourriarone resin of a melting point above '75 C., a remarkable increase in the tensile strength and tear resistanceofthe'vulcanizates. as compared with vulcanizates containing the same-amount of filler and other softeners or no softener, is accomplished. The elongations of the vulcanizates under'givenlst rcss and at the breaking point are also increased; The improvement is of such magnitude that'the'vulcanizatcs produced in accordance with the invention may be employed ,for certain purposes for whichnorijblack butadiene-styrene cop o'ly iner, vulcanizates heretofore had little or no utility. .For example. as described more fully hereinbelow..use .of paracouniarone resin in accordance' 'with the inv m tionincreased the tensile strength of vulcanizates to as much as two or three timesthat ofvulcanizates containing no paracoumarone reslin. Heretofore, non-black butadien styrene cobolym er vulcanizates compounded with' non-bla'ck fillers possessed insuf fiicenttensile s't. r ength or tear resistance or both' for most purposes for which the correspondingnon-blacknaturalrubber vulcanizates were employed. However, on:

black vulcanizate's compounded in acc'c rdance' with the invention, owing totheir improvedfiensile and tear-resisting properties, vniay -be sat factorilyemployed as substitutes for vulc non-black natural rubberin many ap'plic' The vulcan'izates are of relatively high specific gravity andhence are preferably employed gfo'r p poses for which low gravity fvulca ni'za'tes are not required.

Prefera-bly metal oxidefillers of ,iine' or ultra- .fine-particlesize, at leastj'% o'fth'eparticlsof which :do not -.xceed :15 microns ,diameter or thickness, are employed. -Met al oXidef llers ha'ving an average particlesize of l'essith'anl' micron are, particularlypreferred.

The paracoumaron'elresinge nployeq. in accord;

ance ,with t inve'ntion' may 1 m duc e i y. catalytic -pb r fiie e ihe. pol mer-' t ents owns ered from coal- .tarandwater gas tar bydi I in the production of suchtars and oils collecting in manufactured gas distribution and storage ati on oil sobtained 3 systems Examples of such oils are solvent naphtha, crude benzol. toluol, and xylol, light oiland drip oils. Such oils contain varying but substantial amounts of unsaturated resin-formingconstituents such as coumarone, indene, sty-' rene and their homologs, and the resins produced from these oils may containpol ymerization prod-v ucts of two or more of these constituents. The oil fractions employed in making the resins boil within therange of 125 to 200 6., preferably 150 to 200 0., and may contain-minor amounts of polymerizable materials boiling without these ranges. The relative amounts of constituents in commercial resins and the physical properties of. the resins will .depend on several factors, well known in the art such as, frexample, boi ling range of the oil fraction, temperature and time of polymerization, nature and amount of catalyst used, if any. Starting with a givenoil fraction, the composition and properties of resins will depend largely on polymerization conditions, e. g. whether polymerization is effected byheat or by use of a catalyst such as .66 B. sulfuric acid. The expression paracoumarone resin as employed herein includes such catalyst-polymerized and heat-polymerized productsi, As hereinabove pointed out, the resin shouldhave amelting point of at least 75 C., prefera;bly between 100 and 140 C. If desiredresin of the preferred melting point may be'made by blending paracoumarone resin of high melting point, say 160 C., with suflicient high boiling oil, e. g. coal-tar oil boiling within the range of, 200 to 350". C., to produce a mixture of the desired melting point. l

In addition to the fillerand paracoumarone resin the butadiene-styrene copolymer should be compounded withsuitable amounts of vulcanizing agent, preferably sulfur, vulcanizing accelerator and aliphatic fatty acid such as stearic acid. The sulfur is employed in proportions by weight of from 1 to parts, preferably about 2 parts for each 100 parts-of the copolymer. Any accelerator capable of accelerating vulcanization of the copolymer, either alone or in combination with an activating accelerator, may be utilized. Examples of the accelerator types are: aldehyde-amines, such as formaldehyde-aniline reaction products and butyraldehyde-aniline reaction products; guanidines suchas diphenylguanidine and diphenylguanidine oxalate; thiazoles, such as 2-mercaptobenzothiazole, mixed 'dimethyl and ethyl thiazyldisulfides, and benzothiazyl 2 monocyclohexylsulfenamide; thiazolines, such as mercaptothiazoline; thiuram sulfides, such as tetra methylthiuram monosulfide and tetramethylthiuramidisulfide; and (ill/hi0? carbamates, such as n-pentamethylene ammonium pentamethylenedithiocarbamate and zinc dimethyldithiocarbamate.1 From '3 to 'parts by weight of a "metallicjoxide capable of activating the accelerator, preferably 1 about 5 parts of-zincoxide, should'be incorporated in each 100'parts of the copolymeryother' accelerator-activating metallic oxides-are litharge and magnesium oxide. Wherezinc oxide is employed as the filler, it is unnecessary w. utilize additional accelerator-activating 'oxideJ it Dispersion of the paracoumaroriefresin, filler and other compounding ingr'edients'in the but ae diene-styrene copolymer may be accomplished in various ways utilizing conventional equipment of the .type employed foreompounding natural rubber, e. g. rubber mills of theroll type, crinternalmixers such as the Banbury mixer. For

example, a master batchof the copolymer and paracoumarone resin may be made by thoroughly dispersing in the'copolymer a high proportion of paracoumarone resln,.e. g. to IOOparts by weight of the resin for each 100 parts of the copolymer, and milling, a, suffici ,,arnount of the masterbatch,withcopolyme containing no resin and withthe other compounding ingredients to produce a compound containing the desired proportions of the various materials. Alternatively, the sulfur may be first dispersed in the copolymer by milling and the other compounding ingredients then dispersed. If desired, the sulfur may be first dissolved in the paracoumarone resin by heating the sulfur and resin together,

the resultant resinrsulfur blend dispersed in the copolymerfollowed by dispersion of the filler,

.a steam pressure (gauge) activating metal oxide and accelerator. It is desirable, particularly when employing accelerators having a tendency to scorchthe copolymer, toincorporate the accelerator afterthe-pther compounding materials in .order to prevent scorching during the compounding operation,-

, The. following examples are further illustra; tive of the invention: h

Example 1 l I Parts by weight Butadiene-styrene copolymer e 100., Paracoumarone resin (melting point.115-

C.) I Aluminum oxide 25, Zinc oxide ...5 Sulfur -e- Benzothiazyl 2 monocyclohexyl' sulfene- I amide (accelerator) a 1.75

Total 7 ;j 2081.75

The.paracoumai-ine resin employed was produced by polymerization of the resin-forming constituents of coal-tar and water-'gas-tar distillate fractions boiling within therange of to 200 C. with'concentrated (66B.) sulfuric acid and was constituted chiefly ofthe polymers of indene, coumarone and homologs of styrene. The aluminum oxide was a finely divided hydrated product of an average particle size of less than 1 micron'and was employed in amount equal to about 22 parts by volume 'per 100 parts by volume of the butadiene-styrene copolymer. The butadiene-styrene copolymer was milled for 5-to 10 minutes at mill roll temperature of about 130 F. and the sulfur, zinc oxide and aluminum oxide were added while milling at thistemperature. The mill roll temperaturewasthen elevatedto to F. and the paracoumarone resin was addedywithin several minutes the resin was com-- pletely dispersed in the copolymer. Thebatch was then removed from the mill, allowed to cool for several hours, and the accelerator was'then milled into the copolymer at mill roll temperatures below 130 F. The compound was then cured for 30 minutes at307 F. corresponding to of about 60 pounds per square inch.

Example 2 Butadiene-styrene copolymer was compounded and cured for. 30 minutes in the same manner as described in Exampled exceptthat instead of aluminum oxide 115 parts by weight of titanium dioxide were employed as the filler. This amount of titanium dioxide provided about 29.5 parts by volume of the filler for each 100 parts by volume of the copolymer.

Example '3 Example 4 v Parts by weight Butadiene-styrene copolymer 100 Paracoumarone resin (melting point 115- 125 C.) 25 Zinc oxide 150 Sulfur 2 Benzothiazyl 2 monocyclohexyl sulfen- Y amide (accelerator) 1.75

Total 278.75

The ingredients were assembled as described in Example 1 and were then cured for 30 minutes at a temperature of about 307 C. corresponding to a steam pressure of approximately 60 'pounds per square inch.

The vulcanizates of Examples 1', 2 and 4 were light'in color and. the vulcanizate of Example 3 was :read. The vulcanizates were tested both before aging and after aging for 7 days at 70 C. The test results on the vulcanizate of Example 1, which are'illustrative of the results on the vulcanizates of the other examples; are given below. The results of similar tests on a vulcanizate which otherwise contained the same materials and was made by the same procedure as the vulcanizate of Example 1 are also given for purposes of comparison:

It will be observed that thetensile strength of the vulcanizate of Example 1 containing paracoumarone resin and aluminum oxide was much greater than that of the vulcanizate containing the same filler but no paracoumarone resin. The combination of the filler and resin also materially increased the tear resistance and the elongation at the breaking point and for given stress of the vulcanizates. vulcanizates containing the cornbination of the metal oxide fillers and paracoumarone resin of this invention possess properties adapting them for use for most purposes for which non-black vulcanizates are required, while vulcanizates containing such fillers but no paracoumarone resin are not a satisfactory substitute for natural rubber vulcanizates.

Thus it will be seen the invention markedly improves the tensile properties and tear resistance of vulcanizates of butadiene-styrene copolymer compounded with metal oxide fillers, This im provement renders the vulcanizates suitable for many purposes for which non-black vulcanizates of butadiene-styrene copolymer formerly hadno utility owing to their lower tensile strength and tear resistance. The invention provides a;new class of vulcanizates suitable for the manufacture of articles such as drug sundries, e. g. hot water bottles, mechanical rubber goods, footwear and household articles, for whichblackvulcanizates I are not commercially acceptable. The vulcaniv contained no paracoumarone resin but which zates of the invention are primarilyadapted for relatively static uses-in which they arenot subjected to a high degree of repeated fiexure and deformation but. in some cases may be employed for various dynamic purposes.

The resin melting points given herein are de termined by the cube-in-mercury method described in "Protective and Decorative Coatings,

vol. 1, copyright 1941 by J. J. Matiello, pages 366- -36'7, published by John Wiley 8: Sons,'Inc., New York, New York. The'melting points of 75 0., C. and C. determined by this method correspond approximately to melting points of 69 C., 88 C. and 119 C., respectively, as determined by ring and ball method (A. S. T. M. Standard D 36-26). The properties of the rubber iven herein-were determinedby the'following methods: tear'resistance (crescent) by A. SL'T. M. method D 62441T (pounds perinch thickness) tensile strength, modulus and elongation b A. S. T. M. method D 412- 11 (AW die).

Since certain changes may be made without departing from the scope of the'inventlon, it is intended that the above shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A process of making vulcanizates of vulcanizable butadiene-styrene copolymer which comprises compoundin the copolymer with vulcanizing agent, paracoumarone resin of a melting point of at least 75 C. and metal oxide filler selected from the group consisting of aluminum oxide, iron oxide, titanium dioxide and zinc oxide, in proportions of from 15 to 30 parts by weight of the resin to 100 parts by weight of the copolymer and at least 20 parts by volume of filler to 100 parts by volume of the copolymer, and vulcanizing the resultant compound to a resilient vulcanizate.

2. A process as specified in claim 1 in which the filler is hydrated aluminum oxide of an av erage particle size of less than 1 micron.

3. A process as specified in claim 1 in which the filler is red iron oxide of an average particle size less than 1 micron.

4. A process as specified in claim 1 in which the filler is zinc oxide of an average particle size less than 1 micron.

5. A process of making butadiene-styrene copolymer vulcanizates of improved tensile strengthand tear resistance which comprises compounding vulcanizable butadiene-styrene copolymer with from. 20 to 60 parts by volume of metal oxide filler per 100 parts by volume of the copolymer, said filler being selected from the group consisting of aluminum oxide, iron oxide, titanium dioxide and zinc oxide, and 15 to 30 parts by Weight of paracoumarone resin of a melting point of 100 to 140 C. per 100 parts by weight of the copolymer, from 1 to 5 parts by'weight of sulfur per 100 parts by weight of copolymer, and vulcanizing accelerator, the compounded copolymer containing from 3 to 10 parts by weight of an acceleratoractivating metallic-oxide per 100 pgi ts'by weight of'the copolymer, 'and vuicani zing thefr'esultnt poIymer 'non black "vulcaniza tes of improved tens "sile-st'reng'th' and tear resistance which comprises compounding vuloahi'zable bxitadiene=styrene' rco- 'polymerwith from-20'to'6 parts of metallic oxide filler per 100 parts b'y'volume ofthe 'copolymer,

said filler being se'lcted fronithe group consisting ofaluminum oxide, iron oxide-titanium -"dioxide andzinc oxide,'- fiom 15130 30 parts by 'weights of paracoumarone resinof a melting point of from- 100 to 140 C.-per 100, parts by weight of the copolym'er', from 1 105]!)8115 by weight of sulfur per l00 pa'rts'by weight of copolymenan'd vulcanizing accelerator; thec'ompounded copolymerconta'iningfromfi to IO parts by weight -of 8 which thefiiler is hydrated aluminum oxide. at 1eas t907 of which-isofa parbicle sizesnotaexceeding". microns.

1,-9.1 vuicanizate as specified ,incieim 7 21:1

zincpxide per 100 parts byweight" of the copolymer,- and'vulcanizin'g the resultant compound.

. .7. A vulcanizate prepared-by vulcanizing vuldispersed therein vuicanizingfig'ent, paracoumarone 'resin ofwa .me'lting' point of at least 75C.

and metal; oxidefi-I1er1of the group consisting of glumixfium oxide, iron :oxide, titaniumdioxidemnd zinc oxide, said filler being present in amount of ab least '20.vparts;by' volume for 'each 100 c=parts maroxge resin being 7 present in amount of from lfi tgo ggpants by, weight per 1'00zparts byweight of seig opo1ymer,-}arid saidvulcanizing'agentaxid said filler being present 'inemountsto yield a,

zr esilignt vul canizate.

8, ym canizate as specified iI r-cleim '7, in '35 which the "finer is rediz 'on o'xi'de,aa't least 90% of which is of a particle size not; exceeding, 15 m1- crons. I

10. A vulcanizateas *specified in rclaim 'l in which thee-filler is-zin'coxide, a't' 1east. 90% f which is of azparticle size not-yexceeding{15 mi.-

crons. 11. A vulcanizateprepare'd by-vu'lcanizing vulcanizable *butadie-ne-styrene *copolymer having dispersed therein 'pe'r 1 00yparts by weight of, co-

.polymer 15 to '30. parts :by "weight of. paracouma ror e resin of melting point at least (2., l :to :6 parts 'by" weight of sulfur, accelerator, and from 3 to 10 parts by weight of"aceelerator aetivaifiing -metal1ic oxide; an per partstby. volume 01 :copdlymer-ZO to fifljpa'rts by volume aof hydr'ated aluminum oxide filler of an average particle size -'--1e'ssfbhan 1 micron.

REFERENCES CITED The following references are 'of record "in the file or this patent:

IThe compounding of Buna S, by.-I-I;-'L;:Lawrence, -Report No,-42-'4, publishediby -Rubber Chemicals Division of E. I.'du Pont"de iNemours k;Coq Decerr'iber 1942, pages 6-'-& 1 Y Cumai',publishedbyitheBarrttlCompanyfEb. :'-1937,-pages-12 and 13.. i 

